Functional Losses in Ground Spider Communities Due to Habitat Structure Degradation Under Tropical Land-Use Change
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Ecology, 101(3), 2020, e02957 © 2019 by the Ecological Society of America Functional losses in ground spider communities due to habitat structure degradation under tropical land-use change 1,2,13 3 4,5,6 3 1 ANTON M. POTAPOV , NADINE DUPERR E, MALTE JOCHUM , KERSTIN DRECZKO, BERNHARD KLARNER, 5,7 1 8,9 9,10 ANDREW D. BARNES , VALENTYNA KRASHEVSKA , KATJA REMBOLD, HOLGER KREFT , 5,11 12 3 1,10 ULRICH BROSE, RAHAYU WIDYASTUTI, DANILO HARMS, AND STEFAN SCHEU 1J.F. Blumenbach Institute of Zoology and Anthropology, University of Gottingen,€ Untere Karspule€ 2, 37073 Gottingen,€ Germany 2A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninsky Prospect 33, 119071 Moscow, Russia 3Center of Natural History, Zoological Museum, Universitat€ Hamburg, Bundesstraße 52, 20146 Hamburg, Germany 4Institute of Plant Sciences, University of Bern, Hochschulstrasse 6, 3012 Bern, Switzerland 5German Centre for Integrative Biodiversity Research (iDiv), Deutscher Pl. 5E, 04103 Leipzig, Germany 6Institute of Biology, Leipzig University, Deutscher Platz 5e, 04103 Leipzig, Germany 7School of Science, the University of Waikato, Private Bag 3105, 3240 Hamilton, New Zealand 8Botanical Garden of the University of Bern, Altenbergrain 21, 3013 Bern, Switzerland 9Biodiversity, Macroecology & Biogeography, University of Gottingen,€ Busgenweg€ 1, 37077 Gottingen,€ Germany 10Centre of Biodiversity and Sustainable Land Use, Von-Siebold-Strasse 8, 37075 Gottingen,€ Germany 11Institute of Biodiversity, Friedrich Schiller University, Dornburger Strasse 159, 07743 Jena, Germany 12Department of Soil Sciences and Land Resources, Institut Pertanian Bogor (IPB), Jln. Meranti Kampus IPB Darmaga, 16680 Bogor, Indonesia Citation: Potapov, A. M., N. Duperre, M. Jochum, K. Dreczko, B. Klarner, A. D. Barnes, V. Krashevska, K. Rembold, H. Kreft, U. Brose, R. Widyastuti, D. Harms, and S. Scheu. 2020. Functional losses in ground spider communities due to habitat structure degradation under tropical land-use change. Ecology 101(3):e02957. 10.1002/ecy.2957 Abstract. Deforestation and land-use change in tropical regions result in habitat loss and extinction of species that are unable to adapt to the conditions in agricultural landscapes. If the associated loss of functional diversity is not compensated by species colonizing the converted habitats, extinctions might be followed by a reduction or loss of ecosystem functions including biological control. To date, little is known about how land-use change in the tropics alters the functional diversity of invertebrate predators and which key environmental factors may mitigate the decline in functional diversity and predation in litter and soil communities. We applied litter sieving and heat extraction to study ground spider communities and assessed structural character- istics of vegetation and parameters of litter in rainforest and agricultural land-use systems (jungle rubber, rubber, and oil palm monocultures) in a Southeast Asian hotspot of rainforest conver- sion: Sumatra, Indonesia. We found that (1) spider density, species richness, functional diversity, and community predation (energy flux to spiders) were reduced by 57–98% from rainforest to oil palm monoculture; (2) jungle rubber and rubber monoculture sustained relatively high diversity and predation in ground spiders, but small cryptic spider species strongly declined; (3) high spe- cies turnover compensated losses of some functional trait combinations, but did not compensate for the overall loss of functional diversity and predation per unit area; (4) spider diversity was related to habitat structure such as amount of litter, understory density, and understory height, while spider predation was better explained by plant diversity. Management practices that increase habitat-structural complexity and plant diversity such as mulching, reduced weeding, and intercropping monocultures with other plants may contribute to maintaining functional diversity of and predation services provided by ground invertebrate communities in plantations. Key words: Araneae; belowground biodiversity; energy flux; functional diversity; land-use change; oil palm; predation; rainforest; rubber. regions (Gibbs et al. 2010). These changes are driven pri- INTRODUCTION marily by increasing demand in agricultural products, Global deforestation and agricultural intensification such as palm oil and rubber (Corley and Tinker 2016, are causing strong environmental changes in tropical Clough et al. 2016). Recent land-use change is particu- larly prominent in Indonesia, which has experienced the strongest oil palm expansion and is among the leaders in Manuscript received 21 April 2019; revised 31 August 2019; accepted 11 November 2019. Corresponding Editor: Elizabeth the global chart of deforestation rates (Margono et al. T. Borer. 2014, Corley and Tinker 2016, FAOSTAT 2016). Defor- 13 E-mail: [email protected] estation and agricultural expansion in tropical regions is Article e02957; page 1 Article e02957; page 2 ANTON M. POTAPOV ET AL. Ecology, Vol. 101, No. 3 associated with a decline in taxonomic diversity (Fitzher- higher pH (Krashevska et al. 2015, Allen et al. 2016), bert et al. 2008, Drescher et al. 2016) and in the perfor- lower plant diversity, but higher density of understory mance of many ecosystems functions (Dislich et al. compared to rainforest sites (Rembold et al. 2017). 2017). Predation is among the key ecosystem functions These complex changes result in a distinctly different that decline in agricultural landscapes, leading to a habitat structure, suggesting potential turnover of spe- potential weakening of natural pest control (Tscharntke cies and functional traits in soil communities between et al. 2005, Gurr et al. 2017). The effect of tropical land- these different land-use systems (Turner and Foster use change on predation has been studied mostly for ver- 2009). It is not clear if this community change can sus- tebrate predators that control populations of large-sized tain the predation function typically provided by pris- insects, but only a few studies have focused on inverte- tine ecosystems. A number of studies found abundance brate predators that control small-sized litter and soil and species richness in litter and soil arthropods to be fauna (Barnes et al. 2014, Klarner et al. 2017, Potapov lower in oil palm plantations compared to rainforest et al. 2019). (Chung et al. 2000, Fayle et al. 2010, Barnes et al. The relationship between the loss of taxonomic 2014), but selected groups of decomposers, such as diversity and ecosystem functions can be disentangled woodlice and earthworms, may have higher density in with functional traits, i.e., characteristics of individuals monoculture plantations (Hassall et al. 2006, Turner that are relevant to their role in ecosystems and govern and Foster 2009, Potapov et al. 2019). Due to large their response to environmental changes (Vandewalle body size, however, increased earthworm populations et al. 2010, Gagic et al. 2015). Trait-based indices, such in plantations contribute little energy to higher trophic as functional diversity and functional redundancy, pro- levels of the invertebrate food web (Potapov et al. vide proxies for overall changes in ecosystem function- 2019). Such differential responses of various animal ing and resilience (Mason et al. 2005, Laliberteand taxa imply selective exclusion and/or decline of species. Legendre 2010). Land-use change may result in the loss This raises questions on which functional traits con- of species, which cannot adapt or colonize plantations tribute to the resilience against habitat change (Larsen rapidly enough and this may be followed by the loss of et al. 2005), which abiotic and biotic factors drive these functional traits and thereby the functional roles these changes and how differential responses affect the species play. The loss of ecosystem functions thus ecosystem service of predation provided by tropical depends on both the functional redundancy of the orig- invertebrate predator communities. inal community and the magnitude of species loss Predators with a high flexibility may persist under (Flynn et al. 2009). If the original community has many tropical land-use change, maintaining their abundance functionally redundant species, random species loss (e.g., centipedes; Klarner et al. 2017), but little is may initially have only little effect on functional diver- known about other major groups of predators such as sity. However, if there is a factor acting nonrandomly in spiders, despite their importance for ecosystem func- respect to functional traits (or if functional redundancy tioning (Nyffeler and Birkhofer 2017). With more than of the original community is low), functional diversity 48,000 described species (World Spider Catalog; avail- may be lost at a rate that equals or even exceeds species able online),14 spiders (Araneae) are among the most loss (Flynn et al. 2009). These different scenarios result diverse and abundant invertebrate predator taxa world- in a minor or prominent decrease in ecosystem func- wide (Wise 1995, Nyffeler and Birkhofer 2017). Differ- tioning, respectively. On the other hand, plantations ent groups of spiders are adapted to specific are colonized by new species, which replace some spe- microhabitats characterized by differences in food cies that were lost. Such species turnover may compen- availability, vegetation structure and moisture, and sate for the loss of ecosystem functions, or at least employing diverse hunting